I got it from a woman named Adelina upon arriving Ars Magina.
You killed the vampire or at least released the boy, so you should be able to finish the quest. But is it not possible you are talking about
Caroline, not Adelina? That's the name of the woman I got the quest from. You can find her where it says '3' on the picture below. Talk to her again and you get your XP <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />